The Dart VSI2 (speed signal isolator) permits the user to control the output of a variable speed motor drive from any external grounded or ungrounded DC input signal. A single model accepts a wide range of input voltages (0-5 through 0-25VDC or 0-25 through 0-250VDC) AND 4-20mA. The VSI2 incorporates Dart’s unique feedback circuit, which virtually eliminates output changes due to the thermal drift of logic components. The VSI2 is packaged in an aluminum chassis mount housing and contains an on-board power supply for its logic circuit. An electrical isolation rating of 2500Vrms is achieved by the use of an optically isolated IC package. The Dart VSI2 can be used with virtually any motor speed control that has a speed reference circuit of +5 to +15VDC and an input impedance greater than 47K ohms. The output of the VSI2 is a filtered, pulse width modulated signal that is directly proportional to the input speed signal. The wide input range allows the VSI2 to follow signals as low as +0-5V logic levels and up to the 180VDC levels present at the armature leads of a 180VDC motor. By simply connecting the input terminals across the armature leads of a “master motor”, you can use the VSI2 for master/follower operation. The addition of a scaling pot will provide for proportional follower operation.